I like the old look better because it is more alien-looking and less exaggerated with the muscles.

That said, I don't really hate the new look, either. The Protoss are still quite awesome. But in a perfect world they'd go back to the older designs.

I also noticed that the new Protoss seem to look more or less the same, while before, the difference between people of different tribes was very obvious. Look at Zeratul, Tassadar, Fenix, and Aldaris, they all look very different from each other.
Moreover, it seems like now it's very popular to use egiptian ornaments on the chin .